Solid electrolyte, method of preparing the same, and lithium battery including the solid electrolyte

ABSTRACT

A solid electrolyte including: a lithium ion inorganic conductive layer; and an amorphous phase on a surface of the lithium ion inorganic conductive layer, wherein the amorphous phase is an irradiation product of the lithium ion inorganic conductive layer. Also, the method of preparing the same, and a lithium battery including the solid electrolyte.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/666,804, filed on Feb. 8, 2022, which is a continuation of U.S.patent application Ser. No. 16/052,743, filed on Aug. 2, 2018, which hasissued as U.S. Pat. No. 11,276,879, and claims priority to and thebenefit of Korean Patent Application Nos. 10-2017-0099079, filed on Aug.4, 2017, and 10-2018-0090059, filed on Aug. 1, 2018, in the KoreanIntellectual Property Office, and all the benefits therefrom under 35U.S.C. § 119, the contents of which are incorporated herein in theirentirety by reference.

BACKGROUND 1. Field

The present disclosure relates to a solid electrolyte, a method ofpreparing the same, and a lithium battery including the solidelectrolyte.

2. Description of the Related Art

A solid electrolyte used in a lithium metal battery should haveexcellent ionic conductivity, be thermally stable, and be able tosuppress a side reaction between an electrode and a solid electrolyte.Thus a solid electrolyte which is chemically and electro-chemically withrespect to the electrode is desirable. Thus there remains a need for animproved solid electrolyte.

A lithium-lanthanum-zirconium oxide-based solid electrolyte does not,without further modification, have sufficient ionic conductivity due tohigh interfacial resistance with a lithium metal negative electrode.Also, and while not wanting to be bound by theory, it is understood thatpenetration of lithium dendrites-occurs at a grain boundary of thelithium-lanthanum-zirconium oxide-based film when a lithium metalbattery is driven with a high current density. A solid electrolyte withimproved ionic conductivity and resistant dendrite formation is needed.

SUMMARY

Provided are a solid electrolyte and a method of preparing the same.

Provided is a lithium battery including the solid electrolyte.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect, a solid electrolyte includes: a lithium ioninorganic conductive layer; and an amorphous phase on a surface of thelithium ion inorganic conductive layer, wherein the amorphous phaseincludes an irradiation product of the lithium ion inorganic conductivelayer.

According to an aspect, a lithium battery includes a negative electrode;a positive electrode; and the solid electrolyte.

According to an aspect, a method of preparing a solid electrolyteincludes: providing a lithium ion inorganic conductive layer; andirradiating the lithium ion inorganic conductive layer with a laser beamto form an amorphous phase on a surface of the lithium ion inorganicconductive layer to prepare the solid electrolyte.

According to an aspect, a solid electrolyte includes: a lithium ionconductive layer including a lithium ion conductive garnet; and anamorphous lithium-lanthanum-zirconium oxide (LLZO) on a surface of thelithium ion conductive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic view illustrating a structure of an embodiment ofa lithium battery including an electrolyte for a lithium metal battery;

FIG. 2A is a schematic view illustrating a surface of an embodiment ofthe electrolyte for a lithium metal battery;

FIGS. 2B and 2C are each a schematic view illustrating a cross sectionof an embodiment of the electrolyte for a lithium metal battery;

FIGS. 2D and 2E are each a schematic view illustrating a crystal stateof an embodiment of the electrolyte for a lithium metal battery;

FIGS. 3A to 3C are scanning electron microscope (SEM) images showing theresults of SEM analysis of a solid electrolyte prepared according toExample 4;

FIGS. 4A to 4C are SEM images of a solid electrolyte prepared accordingto Example 5;

FIG. 4D is an SEM image showing analysis result of a solid electrolyteprepared according to Example 4;

FIGS. 5A to 5C show the results of transmission electron microscopy andenergy dispersive X-ray (TEM/EDX) analysis of a solid electrolyteprepared according to Example 4, in which FIGS. 5B and 5C each include agraph of intensity (arbitrary units, a.u.) versus energy (electronvolts, eV) and a table providing the results of elemental analysis byenergy dispersive spectroscopy (EDS);

FIGS. 6A to 6D are transmission electron microscope (TEM) images showingthe results of TEM analysis of a solid electrolyte prepared according toExample 4;

FIGS. 7A and 7B are each a graph of electrode potential (Volts vsLi/Li⁺) versus time (hours) showing results of an electrochemicalperformance test of a lithium symmetric cell prepared according toExample 14 and Comparative Example 4;

FIG. 8 is a schematic view illustrating a structure of an embodiment ofa lithium metal battery;

FIGS. 9A and 9B are each a graph of imaginary impedance (Ωcm²) versusreal impedance (Ωcm²) showing interfacial resistance characteristics oflithium metal batteries prepared according to Example 9 and ComparativeExample 3, respectively;

FIGS. 10A and 10B are each a graph of electrode potential (Volts vsLi/Li⁺) versus capacity (milliampere hours per square centimeter,mAh·cm²) showing capacity-dependent electrode potential changes of alithium metal battery prepared according to Example 9 and a lithiummetal battery prepared according to Comparative Example 3, respectively;

FIG. 11 is a graph of capacity (mAh·cm⁻²) and efficiency (percent)versus cycle number showing capacity changes and efficiencycharacteristics of a lithium metal battery prepared according to Example9;

FIG. 12 is a TEM image of a solid electrolyte prepared according toComparative Example 2;

FIG. 13 is a SEM image of a solid electrolyte prepared according toComparative Example 2;

FIG. 14 is a graph of electrode potential (volts vs Li/Li⁺) versuscapacity (mAh·cm⁻²) showing capacity-dependent electrode potentialchanges of a lithium metal battery prepared according to Example 15;

FIG. 15 s a graph of capacity (mAh·cm⁻²) and efficiency (percent) versuscycle number showing capacity changes and efficiency characteristics ofa lithium metal battery prepared according to Example 15;

FIG. 16 shows the fractured cross-sectional SEM image of a fracturedpellets; and

FIG. 17 shows a cross sectional SEM image of a firedlithium-lanthanum-zirconium oxide (LLZO) tape having a thickness ofabout 60 micrometers.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain various aspects. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list. Also, “at least one”does not exclude like elements not named.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” “Or” means “and/or.” As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

A C rate means a current which will discharge a battery in one hour,e.g., a C rate for a battery having a discharge capacity of 1.6ampere-hours would be 1.6 amperes.

Hereinafter, a solid electrolyte for a lithium battery according to anembodiment, a method of preparing the solid electrolyte, and a lithiumbattery including the solid electrolyte will be described in furtherdetail.

According to an embodiment of the present disclosure, there is provideda solid electrolyte comprising a lithium ion inorganic conductive layer;and an amorphous phase on a surface of the lithium ion inorganicconductive layer. The amorphous phase comprises an irradiation productof the lithium ion inorganic conductive layer. In an embodiment theamorphous phase consists of an irradiation product of the lithium ioninorganic conductive layer. The amorphous phase may be in a form of anamorphous film, and the amorphous film may have a thickness of about 5nanometers (nm) to about 5 micrometers (μm), about 10 nm to about 1 μm,or about 20 nm to about 500 nm. The solid electrolyte may furthercomprise a semi-crystalline film comprising a semi-crystalline phase,and the semi-crystalline film may be situated between the lithium ioninorganic conductive layer and the amorphous film. Also, the solidelectrolyte may further comprise a crystalline phase situated betweenthe semi-crystalline film and the amorphous film. The crystalline phasemay be in the form of a crystalline film.

In an embodiment, the amorphous phase may be in a form of a patternedamorphous film. As such, when a pattern is formed on a surface of theamorphous film to prepare a patterned amorphous film, the patternedamorphous film may have a surface area which is about 200 to about 500percent (%) greater than a surface area of the lithium ion inorganicconductive layer, e.g., the lithium ion inorganic conductive layerbeneath the patterned amorphous film. When a surface area of the solidelectrolyte increases, an activation area between the solid electrolyteand a lithium metal negative electrode accordingly increases, therebyreducing interfacial resistance between the solid electrolyte and thelithium metal negative electrode. Thus, when a solid electrolyte isdisposed to be adjacent to at least one of a negative electrode and apositive electrode, the effect of reducing interfacial resistancebetween the solid electrolyte and the at least one of a negativeelectrode and a positive electrode can be obtained. In an embodiment,the patterned amorphous film has a surface area which is about 250 toabout 450%, or about 300 to about 400% greater than a surface area ofthe lithium ion inorganic conductive layer.

As an example of a solid electrolyte used in a lithium battery, alithium-lanthanum-zirconium oxide-based film may be used. However, whenthe lithium-lanthanum-zirconium oxide-based film is used as a solidelectrolyte, interfacial resistance between the solid electrolyte and alithium metal negative electrode increases so that the solid electrolytemay not have sufficient ion conductivity. In particular, when a lithiummetal battery is driven with a high current density, lithium ions maypenetrate the grain boundary of the solid electrolyte and grow therein,to cause a short circuit of the lithium battery.

In this regard, the inventors of the present disclosure have studied andfound that an amorphous film may be disposed on a side of a lithium ioninorganic conductive layer constituting a solid electrolyte to provide asolid electrolyte in which penetration of lithium ions into the grainboundary of the lithium-lanthanum-zirconium oxide-based film and growthof lithium ions therein are suppressed. The amorphous film may bedisposed on both sides of the lithium ion inorganic conductive film. Inan embodiment, the amorphous film of the solid electrolyte may bedisposed to be adjacent to at least one of a positive electrode and anegative electrode during manufacture of a lithium metal battery. Inaddition, the amorphous film may be formed in the shape of a pattern.

As described above, when the lithium ion inorganic conductive layerincludes an amorphous phase on a surface thereof, the effect of removingthe grain boundary from the surface of the solid electrolyte may beobtained. In addition, as the growth of lithium metal or propagation oflithium ions into the solid electrolyte is suppressed, a short circuitcaused by lithium metal may be prevented during a charge/dischargeprocess.

When the solid electrolyte according to an embodiment is used, theinterfacial resistance between the solid electrolyte and lithium metalis reduced, resulting in improved rate performance of a batteryincluding the solid electrolyte. Also, because the occurrence of a shortcircuit caused by lithium is suppressed, the lithium battery has animproved lifespan.

The amorphous phase may be formed by irradiating a laser beam onto thelithium ion inorganic conductive layer. When the lithium ion inorganicconductive layer is irradiated with a laser beam, an amorphous phase maybe formed on a surface of the lithium ion inorganic conductive layer anda surface of the amorphous phase may be physically etched. The amorphousphase may be in the form on an amorphous film on the lithium ioninorganic conductive layer.

Without further modification, lithium-lanthanum-zirconium oxide (LLZO)surfaces are unstable in ambient atmosphere and can form a resistivelayer of lithium carbonate on the surface, and the lithium carbonate candegrade cell performance (see e.g., Cheng, et al., Phys. Chem. Chem.Phys., 2014, 16, 18294, the content of which is incorporated herein byreference in its entirety). While not wanting to be bound by theory, itis understood that in addition to physically etching the surface, lasertreatment beneficially removes the lithium carbonate resistive layer.

The lithium ion inorganic conductive layer of the solid electrolyteaccording to an embodiment can be formed in a way that the grainboundary is formed to a minimum.

FIG. 1 is a schematic view illustrating a structure of an embodiment ofa lithium battery including a solid electrolyte. The lithium battery maybe a lithium metal battery using a lithium metal negative electrode.

Referring to FIG. 1 , a solid electrolyte 12 is disposed on a positiveelectrode 11, and a lithium metal negative electrode 10 is disposed onthe solid electrolyte 12. The solid electrolyte 12 includes a lithiumion inorganic conductive layer 12 a and an amorphous film 12 b that isdisposed on a side of the lithium ion inorganic conductive layer 12 a.The amorphous film 12 b is disposed to be adjacent to the lithium metalnegative electrode 10. The amorphous film comprises the amorphous phase.In FIG. 1 , the amorphous film 12 b is formed only on one side of thesolid electrolyte, but in an embodiment the amorphous film 12 b may beformed on both sides of the solid electrolyte 12.

As shown in FIGS. 2A to 2C, the amorphous film 12 b may be formed in theshape of a pattern on the lithium ion inorganic conductive layer 12 a. Aportion of or an entirely of the amorphous film 12 b may be in the shapeof a pattern. In FIG. 1 , GB refers to grain boundary of the lithium ioninorganic conductive layer 12 a.

The pattern is not particularly limited to any size and shape, and anysuitable pattern may be used as long as a pattern may increase a surfacearea of the solid electrolyte and effectively suppress the volumeexpansion after operation of a lithium battery including the solidelectrolyte. In this regard, a pattern may have a regular or irregularshape.

As non-limiting examples of the shape of the pattern according to anembodiment, the pattern may comprise at least one of a plurality ofperpendicular lines and a plurality of parallel lines [e.g., grid]. Forexample, the plurality of perpendicular lines may be a line type, andthe plurality of parallel lines may be a mesh type (shown in FIG. 2A).

The pattern has an area of from 1 to 900 cm². The perpendicular orparallel lines may have a line width of about 1 micrometer (μm) to about1000 μm, about 5 μm to about 500 μm, or about 10 to about 30 μm.

Referring to FIG. 2A, a line width and a pattern width b indicate apattern size and a pattern width. The line width varies depending on thesize of laser beam. The pattern size may be, for example, in a range ofabout 10 μm to about 10,000 μm, and the pattern width b indicates apattern cycle or a pattern interval, and for example, may be in a rangeof about 1 μm to about 150 μm, about 1 μm to about 50 μm, or about 10 μmto about 30 μm. When the line width a and the pattern width b are withinthe ranges above, a surface area of the solid electrolyte increases sothat the interfacial resistance between the solid electrolyte and atleast one of a positive electrode and a negative electrode may beeffectively decreased and the propagation of lithium ions into the grainboundary of the solid electrolyte and the growth of the lithium ionstherein may be suppressed, thereby effectively preventing growth ofdendrites.

The size and width of the pattern are influenced by the size of laserbeam or the like.

Referring to FIG. 2B, it is confirmed that the pattern may be formedover the entire amorphous film 12 b present on the surface of thelithium ion inorganic conductive layer 12 a. In an embodiment, referringto FIG. 20 , it is confirmed that the pattern may be formed locally onlyon the surface of the amorphous film 12 b.

As shown in FIG. 2B, the pattern may be formed to comprise a pluralityof linear grooves 120, wherein the grooves 120 may have different rangesand depths depending on laser processing conditions. In an embodiment, adepth c of a groove may be in a range from about 0.1 μm to about 20 μm,about 0.5 μm to about 15 μm, or about 1 μm to about 10 μm, and a width dof the grooves may be about 1 μm to about 200 μm, about 10 μm to about150 μm, about 20 μm to about 100 μm.

The amorphous film may include a plurality of grooves and a protrusionbetween the plurality of grooves, wherein the plurality of grooves arespaced apart, on a portion of the lithium ion inorganic conductivelayer. A bottom of the plurality of grooves may be a flat surface, or acurved surface having a radius of curvature.

The plurality of grooves may be periodically disposed.

In an embodiment, a surface area of the solid electrolyte in which apattern is disposed on the surface of the amorphous film may beincreased by about 200% to about 500%, for example, about 300% to about450%, or about 350% to about 400%, as compared to a surface area of thesolid electrolyte in which a pattern is not disposed on the surface ofthe amorphous film. In an embodiment, the surface area of the amorphousfilm may be about 35 cm²/cm³ to about 1×10⁶ cm²/cm³, about 50 cm²/cm³ toabout 1×10⁵ cm²/cm³, or about 100 cm²/cm³ to about 1×10⁴ cm²/cm³. Whenthe solid electrolyte having such surface area characteristics is used,an activation area between the solid electrolyte and at least one of apositive electrode and a negative electrode also increases, and thus alithium battery having improved rate performance may be manufactured. Inthe solid electrolyte according to an embodiment, at least one of aceramic layer, a ceramic glass layer, or both may be formed on theunpatterned surface of the lithium ion inorganic conductive layer. Theceramic layer may be a crystalline film comprising a crystalline phase,and the ceramic glass layer may be a semi-crystalline film comprising asemi-crystalline phase.

The term “a semi-crystalline film” means a mixed phase including acrystalline phase and an amorphous phase, and t includes, for example, aglass-ceramic.

In the solid electrolyte according to an embodiment, the amorphous filmmay have a reduced number of grain boundaries.

In the solid electrolyte according to an embodiment, a semi-crystallinefilm can be further included between the lithium ion inorganicconductive layer and the amorphous film. The semi-crystalline film maybe formed using a melt quenching method, and the semi-crystalline filmmay be formed to have a thickness which is less than that of theamorphous film.

A crystalline film can be further included between the semi-crystallinefilm and the amorphous film. The crystalline film between thesemi-crystalline film and the amorphous film may be the same ordifferent from a crystalline film of the lithium ion inorganicconductive layer. For example, the lithium ion inorganic conductivelayer may be a first crystalline film, and the crystalline film betweenthe semi-crystalline film and the amorphous film may be a secondcrystalline film.

FIGS. 2D and 2E are each are a schematic view illustrating a crystalstate of the solid electrolyte according to an embodiment. Referring toFIG. 2D, the solid electrolyte according to an embodiment may have astructure in which a first crystalline film 210, a semi-crystalline film220, and an amorphous film 230 are sequentially disposed in this statedorder. Referring to FIG. 2E, the solid electrolyte according to anembodiment may have a structure in which a first crystalline film 210, asemi-crystalline film 220, a second crystalline film 215, and anamorphous film 230 are sequentially disposed in this stated order.

In the solid electrolyte, the presence of the amorphous film, thesemi-crystalline film, and the crystalline film may be identified bytransmission electron microscopy/selected area electron diffraction(“TEM/SAED”). For example, through TEM/SAED analysis, when the lithiumion inorganic conductive layer of the solid electrolyte is alithium-lanthanum-zirconium oxide (“LLZO”)-based film, such asLi₇La₃Zr_(1.7)W_(0.3)O₁₂, the formation of the amorphous phase in thesolid electrolyte may be identified. That is, the presence of thesemi-crystalline film between the amorphous phase and the crystallinephase may be confirmed. In addition, a crystalline structure of theLLZO-based film, i.e., a garnet structure, may be identified. UsingTEM/SAED analysis, a ratio of the crystalline film, the amorphous film,and the semi-crystalline film may be directly and/or indirectlyidentified.

A thickness of the amorphous film may be, for example, in a range ofabout 5 nm to about 5 μm, about 50 nm to about 5 μm, about 50 nm toabout 300 nm, or about 5 nm to about 100 nm. A thickness of thesemi-crystalline film may be less than that of the amorphous film, andfor example, may be in a range of about 2 nm to about 3 μm, about 3 nmto about 2 μm, or about 3 nm to about 50 nm.

In an embodiment, a thickness ratio of the amorphous film to thesemi-crystalline film may be in a range of about 1:0.2 to about 1:0.8.

In an embodiment, when a thickness of the amorphous film is about 200nm, the semi-crystalline film may be configured to have a thickness in arange of, for example, about 100 nm to about 150 nm. In an embodiment,when a thickness of the amorphous film is about 2 μm, thesemi-crystalline film may be configured to have a thickness of 1 μm orless.

In polymer electrolyte according to an embodiment, a crystallinity ofthe lithium ion inorganic conductive layer gradually increases in adirection away from the amorphous film. The thickness of the amorphousfilm is less than that of an additional amorphous film, and thethickness of the amorphous film may be, for example, about 5 nm to about5 micrometers (μm), about 10 nm to about 1 μm, or about 20 nm to about500 nm.

An ion conductivity at 60° C. of the solid electrolyte is in a range ofabout 5×10⁻⁴ Siemens per centimeter (Scm⁻¹) or greater.

The lithium ion inorganic conductive layer may include at least onecompound of a garnet compound, an argyrodite compound, a lithium superionic conductor (“LISICON”), a sodium super ionic conductor (“NASICON”),lithium nitride, lithium hydride, perovskite, and lithium halide.

The lithium ion inorganic conductive layer may include, for example, atleast one of a Li-garnet-based ceramic, such as Li_(3+x)La₃M₂O₁₂ wherein0≤x≤5 and M is tellurium (Te), niobium (Nb), or zirconium (Zr), a dopedgarnet-based ceramic, such as Li_(3+x)La₃M₂O₁₂ (wherein 0≤x≤5 and M isTe, Nb, or Zr), Li_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (wherein 0<x<2and 0≤y<3), BaTiO₃, Pb(Zr_(x)Ti_(1−x))O₃ wherein 0≤x≤1 (PZT),Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT) (wherein 0≤x≤1 and 0≤y<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃(PMN-PT), lithium phosphate (Li₃PO₄),lithium titanium phosphate (Li_(x)Ti_(y)(PO₄)₃) (wherein 0<x<2 and0<y<3), lithium aluminum titanium phosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃)(wherein 0<x<2, 0<y<1, and 0<z<3),Li_(1+x+y)(Al_(a)Ga_(1−a))x(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂ (where0≤x≤1, 0≤y≤1, 0≤a≤1, 0≤b≤1), ), lithium lanthanum titanate(Li_(x)La_(y)TiO₃) (wherein 0<x<2 and 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w)) (wherein 0<x<4, 0<y<1, 0<z<1, and0<w<5), lithium nitride (Li_(x)N_(y)) (wherein 0<x<4 and 0<y<2), a SiS₂glass (Li_(x)Si_(y)S_(z)) (wherein 0≤x<3, 0<y<2, and 0<z<4), a P₂S₅glass (Li_(x)P_(y)S_(z)) (wherein 0≤x<3, 0<y<3, and 0<z<7),Li_(3x)La_(2/3−x)TiO₃ (wherein 0≤x≤1/6), Li₇La₃Zr₂O₁₂,Li_(1+y)Al_(y)Ti_(2−y)(PO₄)₃ (wherein 0≤y≤1),Li_(1+z)Al_(z)Ge_(2−z)(PO₄)₃ (wherein 0≤z≤1), Li₂O, LiF, LiOH, Li₂CO₃,LiAlO₂, a Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂ ceramic, Li₁₀GeP₂S₁₂,Li_(3.25)Ge_(0.25)P_(0.75)S₄, Li₃PS₄, Li₆PS₅Br, Li₆PS₅Cl, Li₇PS₅,Li₆PS₅I, Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃, LiTi₂(PO₄)₃, LiGe₂(PO₄)₃,LiHf₂(PO₄)₃, LiZr₂(PO₄)₃, Li₂NH₂, Li₃(NH₂)₂I, LiBH₄, LiAlH₄, LiNH₂,Li_(0.34)La_(0.51)TiO_(2.94), LiSr₂Ti₂NbO₉,Li_(0.06)La_(0.66)Ti_(0.93)Al_(0.03)O₃, Li_(0.34)Nd_(0.55)TiO₃,Li₂CdCl₄, Li₂MgCl₄, Li₂ZnI₄, and Li₂CdI₄.

The lithium ion inorganic conductive layer can be, for example, acompound represented by the Formula 1 or 1a.

Li_(7−x)M¹ _(x)La_(3−a)M² _(a)Zr_(2−b)M³ _(b)O₁₂   Formula 1

Li_(7−x)La_(3−a)M² _(a)Zr_(2−b)M³ _(b)O₁₂   Formula 1a

wherein, in Formula 1, M¹ comprises at least one of gallium (Ga) andaluminum (Al),

in Formulas 1 and 1a, M² comprises at least one of calcium (Ca),strontium (Sr), cesium (Cs), and barium (Ba),

M³ includes at least one of aluminum (Al), tungsten (W), niobium (Nb),and tantalum (Ta), and

0≤x<3, 0≤a≤3, and 0≤b<2.

In Formula 1, x may be from 0.01 to 2.1, for example, 0.01 to 0.99, forexample, from 0.1 to 0.9, and from 0.2 to 0.8. In Formula 1, a may befrom 0.1 to 2.8, for example, 0.5 to 2.75, and b may be from 0.1 to 1,for example, 0.25 to 0.5.

The compound represented by Formula 1 may be, for example, at least oneof Li₇La₃Zr_(1.7)W_(0.3)O₁₂,Li_(4.9)Le_(2.5)Ca_(0.5)Zr_(1.7)Nb_(0.3)O₁₂,Li_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ wherein 0≤δ≤2.5,Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂, Li₇La₃Zr_(1.5)W_(0.5)O₁₂,Li₇La_(2.75)Ca_(0.25)Zr_(1.75)Nb_(0.25)O₁₂, Li₇La₃Zr_(1.5)Nb_(0.5)O₁₂,Li₇La₃Zr_(1.5)Ta_(0.5)O₁₂, Li_(6.272)La₃Zr_(1.7)W_(0.3)O₁₂, orLi_(5.39)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ (0≤δ≤1.11).

In the compound represented by the Formula 1, a dopant may be at leastone of M¹, M², and M³. In the compound represented by the Formula 1a, adopant may be at least one of M² and M³.

An amount of the dopant in the amorphous film can be reduced to be equalor less than about 50%, for example, equal to or less than about 30% orequal to or less than about 10%, or about 0.1 to about 50%, or about 1to about 40%, of an amount of a dopant in an amorphous film obtained byheat treatment only.

In an embodiment, a total amount of a dopant in the amorphous film canbe less than a total amount of a dopant in the crystalline film. In anembodiment, a difference between a total amount of a dopant in thecrystalline film and a total amount of a dopant in the amorphous filmcan be, for example, at least about 0.5 atom % or more, for example,about 1 atom % or more, or at least about 2 atom % to about 3 atom %, orabout 0.5 atom % to about 3 atom %.

In an embodiment, an amount of a dopant in the amorphous film can beabout 30 mole percent (mol %) or less, for example, about 5 mol % orless, about 0.1 mol % or less, about 0.05 mol % or less, or about 0.01mol % to about 30 mol %, or about 0.1 mol % to about 10 mol %, based ona total content of the amorphous film.

In an embodiment, the surface chemistry can be intentionally modified byaddition of a chemical component to enhance the formation of theamorphous surface layer during laser treatment. The addition of, forexample, boron oxide to the surface, can promote formation of anamorphous layer on the LLZO surface.

In the solid electrolyte, a semi-crystalline film is further includedbetween the crystalline film and the amorphous film. In the compoundrepresented by the Formulas 1 and 1a, a dopant may be at least one ofM¹, M², and M³. In the compound represented by the Formula 1a, a dopantmay be at least one of M² and M³.

An amount of the dopant in the amorphous film can be reduced comparedwith an amount of a dopant in the crystalline film. A lithium ioninorganic conductor of the lithium ion inorganic conductive layerincludes a mixture of a first phase compound, which is a major componentsatisfying the stoichiometric composition, and a second phase compound,which is a minor component. The amount of the dopant may be equal to orless than about 1 mol %, based on 100 mol % of the amorphous film.

In an embodiment in which the lithium ion inorganic conductor includesthe compound represented by Formula 1 as the first phase compound, andthe compound represented by Formula 1a as the second phase compound, theamount of the second phase compound may be about 0.1 to about 10 partsby weight, for example, about 0.5 to about 5 parts by weight, based on100 parts by weight of the first phase compound and the second phasecompound.

The amorphous film is a product obtained by irradiating laser beam ontothe lithium ion inorganic conductive layer in a patterning process. Inaddition, a thickness of the amorphous film may be in a range of about50 nm to about 5 μm, for example, about 10 nm to about 500 nm. Inaddition, the lithium ion inorganic conductive layer may be acrystalline film including a crystal grain boundary, and a thicknessratio of the lithium ion inorganic conductive layer to the amorphousfilm may be in a range of about 1:0.001 to about 1:0.2, for example,about 1:0.002 to about 1:0.1, and for example, may be 1:0.004.

The lithium ion inorganic conductive layer according to an embodimentmay include doped LLZO. In the lithium ion inorganic conductive layer,LLZO grains may serve as a crystalline film and an amount of a dopant ofthe doped LLZO is relatively high at the crystal grain boundary.

The solid electrolyte may have an ion conductivity of about 1×10⁻⁷ Scm⁻¹to about 5×10⁻³ Scm⁻¹, for example, about 1×10⁻⁴ Scm⁻¹ to about 1×10⁻³Scm⁻¹. In addition, the solid electrolyte may be a liquid-impermeabledense layer having a porosity of about 30% or less. The porosity of thesolid electrolyte may be, for example, about 25% or less, about 22% orless, about 10% or less, about 5% or less, or about 1% or less, or aporosity of about 0.1% to about 25%, or about 0.1% to about 0.5%.

The term “porosity” is the ratio of the area occupied by the pores tothe total area. The porosity can be obtained by observing the crosssection through scanning electron microscope(SEM) analysis or BETmethod. Porosity can be evaluated, for example, by using an image of ascanning electron microscope in which a solid electrolyte cross sectionis photographed.

A thickness of the solid electrolyte may be in a range of about 1 μm toabout 300 μm, for example, about 2 μm to about 100 μm or about 30 μm toabout 60 μm.

Hereinafter, a method of preparing the solid electrolyte for the lithiumbattery will be described in detail.

The solid electrolyte may be prepared by a method including: performinga step of forming a lithium ion inorganic conductive layer; andperforming a step of disposing an amorphous film on at least one side ofthe lithium ion inorganic conductive layer by irradiating a laser beamonto the lithium ion inorganic conductive layer.

In an embodiment, the laser beam may be irradiated such that a surfacearea of the lithium ion inorganic conductive layer after performing theirradiation of the laser beam in the second step is increased by about10% to about 1,000%, for example, about 10% to about 500% as compared toa surface area of the lithium ion inorganic conductive layer beforeperforming the irradiation of the laser beam in the second step, therebyforming a pattern on the lithium ion inorganic conductive layer.

The forming of the lithium ion inorganic conductive layer may furtherinclude: pressing inorganic lithium ion conductor powder to produce afilm-type product; and performing heat treatment on the film-typeproduct. The heat treatment may be performed at a temperature in a rangeof about 700° C. to about 1,500° C.

According to the conditions described above, the lithium ion inorganicconductive layer with a decreased or minimized grain boundary may beprepared.

After inorganic lithium ion conductor powder is used to provide thefilm-type product, heat treatment may be performed thereon. As such,when the inorganic lithium ion conductor powder is heat treated, changesin a composition of a lithium ion conductor that constitutes a film maybe suppressed during the film manufacturing process.

In an embodiment, the step of forming a lithium ion inorganic conductivelayer may be performed by subjecting the inorganic lithium ion conductorpowder to a hot press process at a temperature of about 700° C. to about1,500° C.

In an embodiment, the step of forming a lithium ion inorganic conductivelayer may be performed by casting a composition including the inorganiclithium ion conductor powder, a solvent, a plasticizer, a binder, and adispersing agent and then heating the resulting product at a temperatureof about 25° C. to about 1,200° C. For example, the solvent may be atleast one of any suitable alcohol or glycol, such as ethanol, butanol,and propylene glycol. The plasticizer may be for example dibutylphthalate, and the binder may for example polyvinyl butyral. Also, asthe dispersing agent, an alkylammonium salt solution of polycarboxylicacid may be used, which is available under the trade name Anti-terra 202(Palmer Holland).

During the irradiation of the laser beam, the laser beam used herein maybe, for example, an ultraviolet (“UV”)-laser. A soft etching process isperformed with a laser beam having a power in a range of about 0.5 watts(VV) to about 15 W, for example, about 0.7 W to about 1 W, a wavelengthin a range of about 300 nm to about 3,000 nm, and a frequency in a rangeof about 100 kilohertz (kHz) to about 1,000 kHz, for example, 57 Hz. Inaddition, the laser beam used herein may have a size in a range of about10 μm to about 10,000 μm, for example, about 20 μm to about 50 μm orabout 30 μm. Here, the term “a size of the laser beam” denotes adiameter of the laser beam. In addition, the laser beam used herein mayhave a laser pulse repetition rate in a range of about 1 kHz to about100 kHz, or a laser pulse repetition rate of about 70 kHz.

During the irradiation of the laser beam, a gas medium or a solid-statemedium may be used. For use as a gas medium, a helium-neon (He-Ne)laser, a carbon dioxide (CO₂) laser, an argon (Ar) laser, or an excimerlaser may be selected. For use as a solid-state medium, neodymium-dopedyttrium aluminum garnet (“Nd:YAG”), Neodymium-doped yttriumorthovanadate (“Nd:YVO₄”), or ytterbium fiber may be selected.

When a laser beam is used, line widths of the laser beam may be formedin various sizes depending on the wavelength of the laser beam. Forexample, a line width of a pattern may reach a minimum line level thatmay be directly patterned by a laser beam. In addition, depending on alaser device, the minimum line width may be sub-micrometers and themaximum line width may be in a range of several hundred micrometers. Inaddition, when output energy of the laser beam is controlled, the shapeof the pattern may be controlled without limitation. When the laser beamis used, a pattern may be formed by partially using a diffractiveoptical element or a mask to control the shape of the beam in favor ofthe pattern.

After a pattern is formed on the surface of the amorphous film by theirradiation with the laser described above, a separate washing andair-blowing process may be additionally performed thereon.

When the solid electrolyte is Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (“LLZO”), asdescribed above, a temperature at the surface of the solid electrolyteis instantaneously raised upon application of the laser thereto and thenmaintained at 25° C. According to such surface quenching effects, theLLZO on the surface of the amorphous film may undergo structural changesfrom a cubic crystal structure to an amorphous crystal structure. When apattern space has a same size as or is smaller than a laser spot size,the entire surface of the solid electrolyte may be treated with thelaser beam. According to the actual TEM image of the cross section ofthe laser-treated LLZO, it is confirmed that the amorphous film isformed on the surface of the LLZO. Such an amorphous film formed on thesurface does not have any grain boundary, which is highly reactive withlithium metal, so that the propagation and growth of lithium ions in thesolid electrolyte may be suppressed. In addition, using EDX analysis onthe solid electrolyte, it is confirmed that a dopant mainly present ongrain boundary of the inorganic solid electrolyte is observed in arelatively small amount at a laser-treated part. Thus, when the LLZOfilm of which a surface is treated with laser is applied as a solidelectrolyte for a lithium metal battery, a lithium metal battery may beoperated for a long period of time without a short circuit.

According to an aspect, a lithium battery includes: a negativeelectrode; a positive electrode, and the solid electrolyte.

The negative electrode may be for example lithium metal negativeelectrode including lithium metal or an alloy of lithium metal. Thelithium battery using the lithium metal negative electrode may be alithium metal battery. The negative electrode may contain a negativeelectrode active material suitable for use in a lithium battery.

The lithium battery may be an all solid battery.

Hereinafter, a lithium metal battery using a lithium metal negativeelectrode as the negative electrode will be described.

The amorphous film of the solid electrolyte may be disposed to beadjacent to the lithium metal negative electrode or the positiveelectrode. In an embodiment, the amorphous film of the solid electrolytemay be, for example, disposed to be adjacent to the lithium metalnegative electrode.

The lithium battery may further include an interlayer between thelithium metal negative electrode and the solid electrolyte. Theinterlayer may serve to increase adhesion between the lithium metalnegative electrode and the solid electrolyte, or may serve to protectthe lithium metal negative electrode. A thickness of the interlayer maybe in a range of about 1 μm to about 10 μm, for example, about 1 μm toabout 2 μm.

The interlayer may include at least one of polyethylene oxide, gold(Au), aluminum oxide (Al₂O₃), lithium aluminate (LiAlO₂), zinc (Zn),silicon (Si), and lithium phosphate.

The lithium metal battery according to an embodiment may further includea protective layer of the lithium metal negative electrode. Any suitablematerial may be used as the lithium protective layer of the lithiummetal negative electrode, and an example thereof includes apoly(oxyethylene methacrylate) (“POEM”) film.

When the lithium metal negative electrode protective film is a POEMfilm, a combination use with a poly(ethylene oxide) (“PEO”) film as aninterlayer may be advantageous in reducing the interfacial resistancebetween the solid electrolyte and the lithium metal negative electrode.

The interfacial resistance between the lithium metal negative electrodeand the solid electrolyte may be in a range of about 10 ohm-squarecentimeters (Ωcm²) to about 500 Ωcm², for example, about 50 Ωcm² toabout 100 Ωcm².

The solid electrolyte according to an embodiment may be utilized as ananolyte of a hybrid electrolyte. The hybrid electrolyte refers to adual-structured electrolyte in which a liquid (or gel) electrolyte isused for a positive electrode electrolyte and a solid electrolyte isused for a negative electrode electrolyte.

FIG. 8 is a schematic view illustrating a structure of a lithium metalbattery according to an embodiment.

Referring to FIG. 8 , a positive active material layer 21 is stacked ona positive current collector 24 to form a positive electrode, and asolid electrolyte 22 a having a structure in which a pattern is formedon each of the both sides thereof is stacked on the positive electrode.In addition, a lithium metal negative electrode 20 and a copper currentcollector 23 are stacked on the solid electrolyte 22 a.

In addition, an interlayer 22 b is disposed between the solidelectrolyte 22 a and the lithium metal negative electrode 20, therebyallowing satisfactory adhesion between the solid electrolyte 22 a andthe lithium metal negative electrode 20. In addition, as shown in FIG. 8, a space between the positive electrode and the solid electrolyte 22 amay be filled with an ionic liquid catholyte (“IL catholyte”). Referencenumber 25 refers to a battery case.

The interlayer 22 b can be, for example, a PEO film or an Au film.

The IL catholyte can include, for example, at least one of an ionicliquid, a polymer-ionic liquid, a lithium salt, and an organic solvent.

The ionic liquid can be any suitable ionic liquid.

The ionic liquid which can be added to the IL catholyte refers to a saltin a liquid state at 25° C. or a fused salt at 25° C. that consists ofonly ions having a melting point equal to or below 25° C. The ionicliquid may be at least one of compounds each including i) a cation of atleast one of ammonium cation, a pyrrolidinium cation, a pyridiniumcation, a pyrimidinium cation, an imidazolium cation, a piperidinumcation, a pyrazolium cation, an oxazolium cation, a pyridazinium cation,a phosphonium cation, a sulfonium cation, a triazolium cation, andmixtures thereof, and ii) at least one anion of BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻,SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, Cl⁻, Br⁻, I⁻,CF₃SO₃ ⁻, (FSO₂)₂N⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, and (CF₃SO₂)₂N⁻.

In an embodiment, the ionic liquid may be at least one ofN-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide,N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide,1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, and1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide.

The polymeric ionic liquid which may be added to the IL catholyte maybe, for example, a polymerization product of ionic liquid monomers, or apolymeric compound. The polymer ionic liquid is highly dissoluble in anorganic solvent, and thus may further improve the ion conductivity ofpolymer layer when further added to the protective layer-formingcomposition.

When the polymeric ionic liquid is prepared by polymerization of ionicliquid monomers as described above, a resulting product from thepolymerization reaction may be washed and dried, followed by anionicsubstitution reaction to have appropriate anions that may improvesolubility in an organic solvent.

In an embodiment, the polymer ionic liquid may include a repeating unitthat includes i) a cation of at least one of an ammonium cation, apyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, animidazolium cation, a piperidinum cation, a pyrazolium cation, anoxazolium cation, a pyridazinium cation, a phosphonium cation, asulfonium cation, a triazolium cation, and mixtures thereof, and ii) atleast one anion of BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻,CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃ ⁻, Al₂Cl₇ ⁻,(CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻, *(CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻,(CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻,(SF₅)₃C⁻, and (O(CF₃)₂C₂(CF₃)₂O)₂PO⁻.

In an embodiment, the polymeric ionic liquid may be prepared bypolymerization of ionic liquid monomers. For example, the ionic liquidmonomers may have a polymerizable functional group such as a vinylgroup, an allyl group, an acrylate group, or a methacrylate group, andmay include a cation of at least one of an ammonium cation, apyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, animidazolium cation, a piperidinum cation, a pyrazolium cation, anoxazolium cation, a pyridazinium cation, a phosphonium cation, asulfonium cation, a triazolium cation, and mixtures thereof, and atleast one of the above-listed anions.

Non-limiting examples of the ionic liquid monomers are1-vinyl-3-ethylimidazolium bromide, a compound of Formula 2, or acompound of Formula 3:

For example, the polymer ionic liquid can be a compound represented by

Formula 4 or a compound represented by Formula 5:

In Formula 4, R₁ and R3 may be each independently a hydrogen, asubstituted or unsubstituted C₁-C₃₀ alkyl group, a substituted orunsubstituted C₂-C₃₀ alkenyl group, a substituted or unsubstitutedC₂-C₃₀ alkynyl group, a substituted or unsubstituted C₆-C₃₀ aryl group,a substituted or unsubstituted C₂-C₃₀ heteroaryl group, or a substitutedor unsubstituted C₄-C₃₀ carbocyclic group; R₂ may be a chemical bond, aC₁-C₃₀ alkylene group, a C₆-C₃₀ arylene group, a C₂-C₃₀ heteroarylenegroup, or a C₄-C₃₀ divalent carbocyclic group; X⁻ indicates an anion ofthe ionic liquid; and n may be from about 500 to 2800.

In Formula 5, Y⁻ is an anion, such as BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻,AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻,Cl⁻, Br⁻, I⁻, SO₄ ² ⁻, CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃⁻, Al₂Cl₇ ⁻, (CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻,(CF₃)₅PF⁻, (CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻,(CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, or (O(CF₃)₂C₂(CF₃)₂O)₂PO⁻; and n can be from 500to 2800.

For example, in Formula 5, Y⁻ may be bis(trifluoromethylsulfonyl)imide(TFSI), bis(fluorosulfonyl)imide, BF₄ ⁻, or CF₃SO₃ ⁻.

The polymeric ionic liquid may include, for example a cation ofpoly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium),poly(1-methacryloyloxy-3-alkylimidazolium), and an anion of CH₃COO⁻,CF₃COO⁻, CH₃SO₃ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, (CF₃SO₂)₃C⁻,(CF₃CF₂SO₂)₂N⁻, C₄F₉SO₃ ⁻, C₃F₇COO⁻, and (CF₃SO₂)(CF₃CO)N⁻.

For example, the compound of Formula 5 may be polydiallydimethylammonium bis(trifluoromethylsulfonyl)imide.

In an embodiment, the polymer ionic liquid may include a low-molecularweight polymer, a thermally stable ionic liquid, and a lithium salt. Thelow-molecular weight polymer may have an ethylene oxide chain. Thelow-molecular weight polymer may be a glyme. Non-limiting examples ofthe glyme are polyethyleneglycol dimethylether (polyglyme),tetraethyleneglycol dimethyl ether (tetraglyme), and triethyleneglycoldimethylether (triglyme). According to an aspect, a solid electrolyteincludes a garnet layer that conducts lithium ions; and an amorphous alithium-lanthanum-zirconium oxide (“LLZO”) surface of the garnet layer.The amorphous LLZO surface has less than 10% of its total area directlycovered by lithium carbonate, and the garnet layer comprises acrystalline garnet, i.e., the crystalline phase having a garnet-typestructure.

The solid electrolyte may be a sheet type, and the amorphous LLZOsurface may cover about 90% or more of the major surface area of thesheet. The interface between the garnet layer and the amorphous LLZO maybe arranged such that the crystallinity of the interface increases asthe distance from the amorphous LLZO surface increases. The depth of theamorphous surface adjacent to the crystalline interface may be, forexample, about 50 nm or more.

Each element of a lithium metal battery including a solid electrolyteaccording to an embodiment, and a method of manufacturing the lithiummetal battery now will be described in further detail.

A positive active material for the positive electrode may include atleast one of lithium cobalt oxide, lithium nickel cobalt manganeseoxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, andlithium manganese oxide, but is not limited thereto. Any suitablepositive active material may be used.

For example, the positive active material may be a compound representedby one of the following formulae: Li_(a)A_(1−b)B′_(b)D₂ (wherein0.90≤a≤1.8, and 0≤b≤0.5); Li_(a)E_(1−b)B′_(b)O_(2−c)D_(c) (wherein0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05), LiE_(2−b)B′_(b)O_(4−c)D_(c) (wherein0≤b≤0.5, and 0≤c≤0.05); Li_(a)Ni_(1−b−c)Co_(b)B′_(c)D_(a) (wherein0.90≤a≤1.8, 0≤c≤0.05, and 0<α≤2);Li_(a)Ni_(1−b−c)Co_(b)B′_(c)O_(2−α)F′_(α) (wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)B′_(c)D_(α) (wherein0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2);Li_(a)Ni_(1−b−c)Mn_(b)B′_(c)O_(2−α)F′_(α) (wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≤a≤1.8,0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂(wherein 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1),Li_(a)NiG_(b)O₂ (wherein 0.90≤a≤1.8, and 0.001≤b≤0.1); Li_(a)CoG_(b)O₂(wherein 0.90≤a≤1.8, and 0.001≤b≤0.1), Li_(a)MnG_(b)O₂ (wherein0.90≤a≤1.8, and 0.001≤b≤0.1); Li_(a)Mn₂G_(b)O₄ (wherein 0.90≤a≤1.8, and0.001≤b≤0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiO′O₂; LiNiVO₄;Li_((3−f))J₂(PO₄)₃ (wherein 0≤f≤2); Li_((3−f))Fe₂(PO₄)₃ (wherein 0≤f≤2);and LiFePO₄.

In the formulae above, A is at least one of nickel (Ni), cobalt (Co),and manganese (Mn), B′ is at least one of aluminum (Al), nickel (Ni),cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe), magnesium (Mg),strontium (Sr), vanadium (V), and a rare earth element; D is at leastone of oxygen (O), fluorine (F), sulfur (S), and phosphorus (F)); E isat least one of cobalt (Co), and manganese (Mn), F′ is at least one offluorine (F), sulfur (S), and phosphorus (F)); G is at least one ofaluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg),lanthanum (La), cerium (Ce), strontium (Sr), and vanadium (V); Q is atleast one of titanium (Ti), molybdenum (Mo), and manganese (Mn), I′ isat least one of chromium (Cr), vanadium (V), iron (Fe), scandium (Sc),and yttrium (Y); and J is at least one of vanadium (V), chromium (Cr),manganese (Mn), cobalt (Co), nickel (Ni), and copper (Cu).

For example, the positive active material may be a compound representedby Formula 6, a compound represented by Formula 7, a compoundrepresented by Formula 8, or a compound represented by Formula 9

Li_(a)Ni_(b)Co_(c)Mn_(d)O   (Formula 6),

wherein, in Formula 6, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0≤d≤0.5;

Li₂MnO₃   (Formula 7);

LiMO₂   (Formula 8);

wherein, in Formula 8, M can be Mn, Fe, Co, or Ni, and

Li_(a)Ni_(b)Co_(c)Al_(d)O₂   (Formula 9),

wherein, in Formula 9, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0≤d≤0.5.

The positive electrode of the lithium metal battery may be manufacturedas follows.

A positive active material, a binder, and a solvent are mixed to preparea positive active material composition. A conducting agent may befurther added into the positive active material composition. Thepositive active material composition is directly coated on a metalliccurrent collector and dried to prepare a positive electrode plate. In anembodiment, the positive active material composition may be cast on aseparate support to form a positive active material film, which may thenbe separated from the support and then laminated on a metallic currentcollector to prepare a positive electrode plate.

The binder is a composition that contributes to binding of an activematerial and a conductive material with a current collector, and thus anamount of the binder added may be from about 1 part by weight to about50 parts by weight, based on 100 parts by weight of the total weight ofthe positive active material. Non-limiting examples of the binderinclude polyvinylidene fluoride (“PVDF”), polyvinyl alcohol,carboxymethylcellulose (“CMC”), starch, hydroxypropylcellulose,reproduced cellulose, polyvinylpyrrolidone, polytetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymer(“EPDM”), sulfonated EPDM, styrene butadiene rubber, fluorine rubber,and various copolymers. The amount of the binder may be from about 2parts by weight to about 5 parts by weight, based on 100 parts by weightof the total weight of the positive active material. When the content ofthe binder is within this range, a binding force of the positive activematerial layer to the current collector may be satisfactory.

The conducting agent may be any suitable material that does not causechemical change in the lithium metal battery and has conductivity.Non-limiting examples of the conducting agent include graphite such asnatural graphite or artificial graphite; carbonaceous materials, such ascarbon black, acetylene black, Ketjen black, channel black, furnaceblack, lamp black, or summer black; conductive fibers, such as carbonfibers or metal fibers; carbon fluoride; metal powder, such as aluminumor nickel powder; conductive whiskers, such as zinc oxide or potassiumtitanate; a conductive metal oxide, such as a titanium oxide; and aconductive material, such as a polyphenylene derivative.

The amount of the conducting agent may be from about 1 part by weight toabout 10 parts by weight, for example, from about 2 parts by weight toabout 5 parts by weight, based on 100 parts by weight of the totalweight of the positive active material. When the amount of theconducting agent is within any of these ranges, the final positiveelectrode may have good conductivity characteristics.

A non-limiting example of the solvent is N-methylpyrrolidone.

The amount of the solvent may be from about 100 parts by weight to about2,000 parts by weight, based on 100 parts by weight of the positiveactive material. When the amount of the solvent is within this range, aprocess for forming the positive active material layer may be easilycarried out.

The amounts of the positive active material, the conducting agent, thebinder, and the solvent may be any suitable levels for the manufactureof lithium metal batteries. At least one of the conducting agent, thebinder, and the solvent may be omitted depending on the use andstructure of a lithium metal battery.

The negative electrode may be, for example, a lithium metal thin film ora lithium metal alloy thin film, as described above.

A lithium metal alloy for the negative electrode may include lithium,and a metal/metalloid alloyable with lithium. Examples of themetal/metalloid alloyable with lithium are Si, Sn, Al, Ge, Pb, Bi, Sb, aSi—Y′ alloy (wherein Y′ is at least one of an alkaline metal, analkaline earth metal, a Group 13 to Group 16 element, a transitionmetal, and a rare earth element, except for Si), a Sn—Y′ alloy (whereinY′ is at least one of an alkaline metal, an alkaline earth metal, aGroup 13 to Group 16 element, a transition metal, and a rare earthelement, except for Sn). Y may be at least one of Mg, Ca, Sr, Ba, Ra,Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb,Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge,P, As, Sb, Bi, S, Se, Te, and Po.

The solid electrolyte according to an embodiment of the presentdisclosure is used as the electrolyte. The amorphous film of the solidelectrolyte is disposed to be adjacent to the lithium metal negativeelectrode or positive electrode. For example, the amorphous film of thesolid electrolyte is disposed to be adjacent to the lithium metalnegative electrode. The lithium metal battery comprises an interlayerbetween the lithium metal negative electrode and the solid electrolyte.The interlayer. The interlayer acts to increase the adhesion between thenegative electrode and the solid electrolyte.

The lithium metal battery further comprises a protective layer on thelithium metal negative electrode in addition to the interlayer. Thelithium metal battery according to an embodiment of the presentdisclosure includes a separator and/or a lithium salt-containingnon-aqueous electrolyte suitable for use in lithium metal batteries.

The separator may be an insulating thin film having high ionpermeability and high mechanical strength. The separator may have a porediameter of about 0.01 μm to about 10 μm, and a thickness of about 5 μmto about 20 μm. Non-limiting examples of the separator are olefin-basedpolymers, such as polypropylene, and sheets or non-woven fabric made ofglass fiber or polyethylene. When a lithium metal battery uses a solidpolymer electrolyte, the solid polymer electrolyte may also serve as theseparator.

For example, the separator may be a monolayer or a multilayer includingat least two layers of polyethylene, polypropylene, polyvinylidenefluoride, or a combination thereof. For example, the separator may be amixed multilayer, such as a two-layer separator ofpolyethylene/polypropylene, a three-layer separator ofpolyethylene/polypropylene/polyethylene, or a three-layer separator ofpolypropylene/polyethylene/polypropylene. The separator may include anelectrolyte including a lithium salt and an organic solvent.

The lithium salt-containing nonaqueous electrolyte may include anonaqueous electrolyte and a lithium salt. The nonaqueous electrolytemay be a nonaqueous liquid electrolyte, an organic solid electrolyte, oran inorganic solid electrolyte.

The nonaqueous liquid electrolyte may include an organic solvent. Theorganic solvent may be any suitable organic solvent. For example, theorganic solvent may be at least one propylene carbonate, ethylenecarbonate, fluoroethylene carbonate, butylene carbonate, dimethylcarbonate, diethyl carbonate, methyl ethyl carbonate, methylpropylcarbonate, ethylpropyl carbonate, methylisopropyl carbonate, dipropylcarbonate, dibutyl carbonate, chloroethylene carbonate, benzonitrile,acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, y-butyrolactone,1,3-dioxolane, 4-methyldioxolane, N,N-dimethyl formamide, N,N-dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, anddimethyl ether.

For example, the lithium salt may be at least one of LiPF₆, LiBF₄,LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃,LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x andy are natural numbers), LiCI, and LiI. For example, to improvecharge-discharge characteristics and resistance to flame in a lithiummetal battery, pyridine, triethylphosphate, triethanolamine, cyclicether, ethylene diamine, n-glyme, hexamethyl phosphoramide, nitrobenzenederivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammoniumsalt, pyrrole, 2-methoxyethanol, or aluminum trichloride may be added tothe nonaqueous electrolyte. In an embodiment, to provide nonflammablecharacteristics, a halogen-containing solvent such as carbontetrachloride, ethylene trifluoride, or the like may be further added tothe nonaqueous electrolyte, if desired.

For example, the lithium metal battery according to an embodiment mayhave improved capacity and improved lifetime characteristics, and thusmay be used in a battery cell for use as a power source of a smalldevice, and may also be used as a unit battery of a medium-large sizebattery pack or battery module that include a plurality of battery cellsfor use as a power source of a medium-large size device.

Examples of the medium-large size device are electric vehicles (“EVs”),including hybrid electric vehicles (“HEVs”) and plug-in hybrid electricvehicles (“PHEVs”), electric two-wheeled vehicles, including E-bikes andE-scooters; power tools; power storage devices; and the like, but arenot limited thereto.

Hereinafter, the present disclosure will now be described in detail withreference to the following examples. However, these examples are notintended to limit the scope of the one or more embodiments of thepresent disclosure.

EXAMPLES Example 1: Preparation of Lithium-Lanthanum-Zirconium Oxide(“LLZO”) Film

Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO) powder wasuniaxially-pressed with a pressure of about 200 megapascals (MPa) into apellet form. Subsequently, the pellet was covered with mother powder(i.e., Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂), and then, heat treatment wasperformed thereon at a temperature of 1,200° C. for 4 hours. A surfaceof the pellet obtained therefrom was polished to form alithium-lanthanum-zirconium oxide (“LLZO”) film having a thickness ofabout 500 micrometers.

Example 2: Preparation of Lithium-Lanthanum-Zirconium Oxide (“LLZO”)Film

Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO) powder was hot pressed intoa thick pellet with a pressure of 20 MPa and temperature of 1,150° C.for 2 hours (hrs). Subsequently, the pellet was wire-saw-sliced intoabout 350 micrometer thick discs. Some of the discs were polished to 250micrometer or 150 micrometer thinner discs. The pellets were ultrasoundcleaned in hexane to remove cutting and polishing fluids and dust.Finally, the pellets were laser cut to needed size and shape to form theLLZO film having a thickness of about 60 micrometers (μm).

FIG. 16 shows the fractured cross-sectional SEM image of the pellets.

Example 3: Preparation of LLZO Film

A Li_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ (0≤δ≤1.6) film was prepared bya tape casting method. The Li_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂(0≤δ≤1.6) powder was mixed in the tape casting slurry listed in Table 1.The slip was then casted into a thin film. After drying, the film wasplaced in a Pt box lined with Li_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂(0≤δ≤1.6) powder but containing 30% excess Li to LLZO tape. After placedon the LLZO tape on the flat powder bed, more of theLi_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ (0≤δ≤1.6) powder was usedcovered on the tape. The box with the tape was subjected to heattreatment with the following schedule:

Heating from about 25° C. to 1050° C., heating rate of 300° C/hour (hr);

Hold at about 1050° C. for 2 hrs; and

cooling from about 1050° C. to 25° C., cooling rate of 200° C/hr.

FIG. 17 shows a cross sectional SEM image of the fired LLZO tape, i.e.,a fractured LLZO membrane made by tape casting having a thickness ofabout 60 micrometers.

TABLE 1 Ingredient Weight (grams) LLZO garnet powder (0.6 17micrometers) solvent: a mixture of ethanol (77 33 volume percent (vol%)), butanol (19 vol %), and propylene glycol (4 vol %) Dibutylphthalate 1.88 PVB-B79 2.0 Anti-terra 202 (dispersant) 0.34

Example 3a: Preparation of LLZO Film

LLZO film was prepared as in Example 1, except thatLi_(4.9)La_(2.5)Ca_(0.5)Zr_(1.7)Nb_(0.3)O₁₂ (Ca, Nb-doped LLZO) powderwas used instead of Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO) powder.

Example 3b: Preparation of LLZO Film

LLZO film was prepared as in Example 1, except thatLi_(4.9)Ga_(0.5+δ)La_(2.5)Zr_(1.7)Nb_(0.3)O₁₂ (0≤δ≤1.6)(Ga, Nb-dopedLLZO) powder was used instead of Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-dopedLLZO) powder.

Example 3c: Preparation of LLZO Film

LLZO film was prepared as in Example 1, except thatLi_(6.272)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO) powder was used insteadof Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO) powder.

Example 3d: Preparation of LLZO Film

LLZO film was prepared as in Example 1, except thatLi_(5.39)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂(00δ≤03+pt (Ga,W-doped LLZO)powder was used instead of Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ (W-doped LLZO)powder.

Example 3e: Preparation of LLZO Film

LLZO film was prepared as in Example 1, except that the heat treatmentwas performed at a temperature of 1,140° C. for 2 hours.

Example 4: Preparation of Solid Electrolyte

The LLZO film having a thickness: about 350 μm was obtained in the samemanner as in Example 1, except that the thickness of the LLZO film wasadjusted to be about 350 μm .The LLZO film (having a thickness of about350 μm) of Example 1 was irradiated with an ultraviolet (“UV”)-laser(neodymium-doped yttrium aluminum garnet (“Nd:YAG”) laser) so that upperand lower portions of the LLZO film were surface-treated. Accordingly, asolid electrolyte having a mesh or grid type pattern (and an area of 1centimeter (cm)×1 cm) on the upper and lower portions was formed. Themesh or grid type pattern had a spacing interval between laser lines(center-on-center) of about 50 micrometers, between laser lines(edge-to-edge) of about 20 micrometers, and a laser size or linethickness of about 30 micrometers. To minimize surface reactions betweenthe solid electrolyte and moisture in the air, the surface treatmentassociated with the laser irradiation was performed in a dry-airatmosphere to prepare a solid electrolyte.

Conditions for the UV laser irradiation are listed in Table 2.

TABLE 2 Process variable Condition Wavelength 355 nanometers (nm) Laserbeam spot size 30 μm Laser power About 1 watt (W) Frequency 57 hertz(Hz) Scanning speed 2,000 millimeters per second (mm/s) Laser pulserepetition rate 70 kilohertz (kHz)

Example 4a: Preparation of Solid Electrolyte

Example 4 was repeated except that the LLZO film of Example 3a was usedinstead of the LLZO film of Example 1.

Example 4b: Preparation of Solid Electrolyte

Example 4 was repeated except that the LLZO film of Example 3b was usedinstead of the LLZO film of Example 1.

Examples 5: Preparation of Solid Electrolytes

Solid electrolytes was prepared as in Example 4, except that theconditions for the UV laser irradiation were changed such that solidelectrolyte having a mesh type pattern having an interval of about 150μm was prepared. The mesh type pattern was formed on both upper andlower portions of the corresponding solid electrolyte.

Example 6: Preparation of Solid Electrolyte

Solid electrolyte was prepared as in Example 4, except that theconditions for the UV laser irradiation were changed such that solidelectrolyte having a mesh type pattern having an interval of about 30 μmwas prepared.

Example 7: Preparation of Solid Electrolyte

Solid electrolytes were prepared as in Example 4, except that thecondition for the UV laser irradiation were changed such that only onesurface of the LLZO film was surface-treated to form solid electrolytehaving a mesh type pattern having an interval of about 30 μm.

Example 8: Preparation of Solid Electrolyte

Example 5 was repeated except that the LLZO film having a thickness of60 μm of Example 2 was used instead of the LLZO film having a thicknessof about 350 μm of Example 1. A solid electrolyte having a mesh typepattern having an interval of about 50 μm and an area of 1 cm×1 cm wasformed on both the upper and lower surfaces of the solid electrolyte.

Example 9: Preparation of Lithium Metal Battery

First, a positive electrode was prepared as follows.

LiCoO₂ (“LCO”), a conducting agent (CA) (Super-P, Timcal Ltd.),polyvinylidene fluoride (“PVDF”), and N-methylpyrrolidone solvent weremixed to obtain a composition for forming a positive active materiallayer. A mixing weight ratio of the LCO to the conducting agent (“CA”)to the PVDF in the composition was, for example, LCO:CA:PVDF=97:1.5:1.5.The amount of the N-methylpyrrolidone solvent was about 137 g when anamount of the LCO was 97 g.

An upper portion of an aluminum foil (having a thickness of about 15 μm)was coated with the composition for forming a positive active materiallayer, dried at a temperature of 25° C., and then, vacuum-dried at atemperature of 110° C., to produce a positive electrode.

The resulting positive electrode was immersed in an ionic liquid, e.g.,N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl) imide (“PYR₁₃FSI”)(the structure of the PYR₁₃ ⁺ cation has the accompanying formula), anda gold (Au) layer was stacked thereon to a thickness of about 1.5 μm.Then, the solid electrolyte of Example 4, a lithium metal negativeelectrode (having a thickness of about 20 μm), and a current collector(copper foil) were stacked on an upper portion of the positive electrodeincluding the gold (Au) layer stacked thereon, to produce a lithiummetal battery (i.e., a hybrid electrolyte cell) having a stackedstructure of FIG. 8 .

A liquid electrolyte was added to a space between the positive electrodeand the lithium metal negative electrode, thereby preparing a lithiummetal battery. The liquid electrolyte was an electrolyte having 1.0 MLiN(SO₂F)₂ (hereinafter, referred to as LiFSI) dissolved in a mixedsolvent containing 1.2-dimethoxyethane (“DME”) and1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (“TTE”) at avolume ratio of 2:8.

Examples 10 to 13: Preparation of Lithium Metal Batteries

Lithium metal batteries were prepared as in Example 9, except that solidelectrolytes of Examples 5 to 8 were used instead of the solidelectrolyte of Example 4, respectively.

Example 14: Preparation of Lithium Symmetric Cell

Both sides of the solid electrolyte of Example 5 were each sputteredwith Au to form a Au film. Subsequently, a lithium metal negativeelectrode was stacked on an upper portion of the Au film, and a heattreatment was performed thereon at a temperature of about 200° C. Then,a resting time was maintained at the same temperature for 20 minutes toallow adhesion of molten Li to the LLZO solid electrolyte, therebypreparing a lithium symmetric cell. To minimize the formation ofcontaminants on the surface of the molten Li, the preparation of thelithium symmetric cell was performed in a glove box in an argon gasatmosphere.

Example 15: Preparation of Lithium Metal Battery

A lithium metal battery was prepared as in Example9, except that apolyethylene film was stacked instead of the gold (Au) layer.

Comparative Example 1: Preparation of Solid Electrolyte

Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂ prepared by Example 1 was wire-saw-slicedinto 500 μm discs. Then, a Li₇La₃Zr₂O₁₂ amorphous oxide film having anaverage thickness of 0.5 μm was deposited on both surfaces of the discby sputtering to obtain a solid electrolyte structure.

The solid electrolyte structure was placed between two stainless steelplates, and an impedance analyzer was connected to measure alternatingcurrent impedance. The measured lithium ion conductivity of the solidelectrolyte was 1×10⁻⁶ siemens per centimeter (S/cm).

According to Comparative Example 1, the amorphous phase was presentinside the solid electrolyte so that the conduction oflithium-disrupted. Thus, it was confirmed that the solid electrolytes ofComparative Example 1 showed low ion conductivity as compared to thesolid electrolyte of Example 1.

Comparative Example 2: Preparation of Solid Electrolyte

Precursors, such as LiOH.H₂O, Al₂O₃, GeO₂, and NH₄H₂PO₄, were weighedand mixed under stoichiometric conditions to produce 3 g of a ceramicmaterial.

Then, the mixture was added to a platinum crucible, and was heat-treatedat a temperature of about 500° C. for 2 hours. Next, the resultingpowder was dry-milled in a ball mill with gate balls for 1 hour. Then,the resulting powder was heat-treated in a platinum crucible at atemperature of about 900° C. for 2 hours, followed by being crushedagain under the same conditions as before to prepare a lithium aluminumgermanium phosphate (“LAGP”) powder. 1 g of the lithium aluminumgermanium phosphate (“LAGP”) powder was inserted into the mold andsubjected to uniaxial pressing under a pressure of 4 tons to obtainpellets. The pellets were heat-treated at 950° C. for 2 hours to obtaina LAGP layer having a thickness of 700pm and a density of 85%.

The above procedure was repeated to obtain three LAGP layers, and thethree LAGP layers were thus formed to measure the ion conductivity,under three conditions i)before laser beam irradiation, ii)after laserbeam irradiation, or iii) after heat treatment for recrystallization,respectively.

The transmission electron microscopy/energy dispersive X-ray (TEM/EDX)analysis was performed on the layers prepared according to ComparativeExample 2, and the results are shown in FIGS. 12 and 13 .

Referring to the analysis results, it was confirmed that, when a filmwas prepared using crystalline LLZO particles or precursors and a solidelectrolyte film was finally prepared using laser only withoutperforming high-temperature heat treatment (1,000° C. or higher) asshown in Comparative Example 2, the resulting amorphous film did nothave high density. When crystalline LLZO particles were used in a slurryform (using toluene/ethanol solvent) and a tape casting process andlaser treatment was performed over the entire particles in the slurryform, the resulting film did not have high density, and had a porosityof 22% or less. In addition, due to weak adhesion between the particles,when a laser beam was applied, the cohesion between the particles wasdisrupted before melting. Thus, a liquid-impermeable non-crystallineLLZO film was not formed, and accordingly, was not use in ahybrid-structured electrolyte cell. In addition, as shown in EvaluationExample 8, the solid electrolyte that was prepared showed very low ionconductivity of less than 10⁻⁶ S/cm.

Comparative Example 3: Preparation of Lithium Metal Battery

A lithium metal battery was prepared as in Example 9, except that thesolid electrolyte of Comparative Example 1 was used instead of the solidelectrolyte of Example 4.

Comparative Example 4: Preparation of Lithium Symmetric Cell

Lithium symmetric cell was prepared as in Example 14, except that thesolid electrolytes of Comparative Example 1 was used instead of thesolid electrolyte of Example 5.

Comparative Example 5: Preparation of Lithium Symmetric Cell

Lithium symmetric cell was prepared in the same manner as in Example 14,except that the solid electrolytes of Comparative Example 2 were usedinstead of the solid electrolyte of Example 5.

Evaluation Example 1. Scanning Electron Microscopic (“SEM”) Analysis

1) Solid electrolytes of Examples 4 and 5.

The SEM analysis was performed on the solid electrolytes of Examples 4and 5.

An SEM used herein was SU-8030 manufactured by Hitachi Company. SEMimages of the solid electrolyte of Example 4 were shown in FIGS. 3A to3C, and SEM images of the solid electrolyte of Example 5 were shown inFIGS. 4A to 4C.

Referring to the figures, it was confirmed that, due to the surfacetreatment performed on the LLZO solid electrolyte using the laserirradiation, the surface area of the LLZO solid electrolyte increased.Accordingly, it was also confirmed that, when the LLZO solid electrolytewas in contact with a lithium metal negative electrode, the activationarea of the LLZO solid electrolyte also increased.

2) Solid Electrolyte of Example 7

The SEM analysis was performed on the solid electrolyte of Example 7under the same conditions as the SEM analysis performed on the solidelectrolytes of Examples 4 and 5. The analysis result of the solidelectrolyte prepared according to Example 4 is shown in FIG. 4D.

Referring to FIG. 4D, it was confirmed that the surface of the solidelectrolyte of Example 4 had an irregular shape. The solid electrolyteof Example 5 exhibited almost the same analytical results as the solidelectrolyte of Example 4.

Evaluation Example 2: Transmission Electron Microscopy/Energy DispersiveX-Ray (“TEM/EDX”) Analysis

The TEM/EDX analysis was performed on the solid electrolyte of Example4. The amorphous film of the solid electrolyte of Example 4 at EDS Spot1 and EDS Spot 2 (see FIG. 5A) was subjected to the TEM/EDX analysis.The EDS results for Spot 1 are provided in FIG. 5B, and the EDS resultsfor Spot 2 are provided in FIG. 5C.

Referring to the analysis, it was confirmed that an amount of tungsten,which serves as a dopant in the non-crystalline phase, was reduced to 1atomic % or less in the solid electrolyte of Example 4. Thus, when thesolid electrolyte of Example 4 or the like was used, a lithium metalbattery including the solid electrolyte may have improved durability.

Evaluation Example 3: TEM Analysis 1) Solid Electrolyte of Example 4

The state of the solid electrolyte of Example 4 was observed using a TEMfor analysis. An analyzing device used herein was Titan cubed 60-300manufactured by FEI, and the analysis results are shown in FIGS. 6A to6D.

FIGS. 6B to 6D are each an enlarged view showing A1, A2, and A3 regionsof FIG. 6A. As shown in FIG. 6A, an amorphous film was formed on thesurface of the solid electrolyte, and a garnet-structured crystallinephase layer was formed inside the amorphous film (see FIG. 6C). Inaddition, the presence of a semi-crystalline phase film was observedbetween the amorphous film and the crystalline phase layer (see FIG.6B).

Evaluation Example 4: Electrochemical Performance

The Li-deposition/stripping test was performed on the lithium symmetriccells of Example 14 and Comparative Example 4 by using a constantcurrent method for every 1 hour. The electrochemical performance of thelithium symmetric cells of Example 14 and Comparative Example 4 wastested as current density was increased stepwise from 0.2 milliampereper square centimeter (mA/cm²) to 1.8 mA/cm², and the results are shownin FIGS. 7A and 7B.

Referring to FIGS. 7A and 7B, shortage signals were observed at 0.6mA/cm² in the lithium symmetric cell of Comparative Example 4(unpatterned-LLZO). However, it was confirmed that the lithium symmetriccell of Example 14 (laser-patterned LLZO) was more stable againstshorting, without shortage until reaching 1.8 mA/cm².

Evaluation Example 5: Interfacial Resistance

Regarding the lithium metal batteries of Example 9 and ComparativeExample 3, an impedance analyzing device (Solartron 1260AImpedance/Gain-Phase Analyzer) was used to measure resistance at atemperature of 25° C. according to the 2-probe method. The conditionsincluded an amplitude of ±10 millivolts (mV) and a frequency range from0.1 Hz to 1 MHz. Nyquist plots of the impedance measurement resultsobtained at 24-hour elapsed time after the preparation of the lithiummetal batteries of Example 9 and Comparative Example 3 were shown inFIGS. 9A and 9B, respectively.

Referring to FIGS. 9A and 9B, it was confirmed that, as a result of theimpedance measurement, the overall interfacial resistance of the cellwas reduced from about 100 square centimeters (Ωcm²) to about 25 Ωcm²upon the laser patterning. Such reduction of the overall interfacialresistance was believed to be caused by the increased active areaassociated with the Li deposition/stripping reactions upon the laserpatterning.

Evaluation Example 6: Charge/Discharge Characteristics

-   Lithium metal batteries (Hybrid electrolyte cells) of Example 9 and    Comparative Example 3

The charge/discharge characteristics of the lithium metal batteries ofExample 9 and Comparative Example 3 were evaluated as follows. Acharge/discharge cycle was driven at a current density of 0.3 mA/cm².

For the first charge/discharge of the lithium metal battery of Example9, the cell was charged with a constant current of 0.1 C until a voltagethereof reached 4.1 V, and maintained at a constant voltage until acurrent thereof reached 0.05 C. Once the cell charging was completed,after a quiet (open circuit) period of about 10 minutes, constantcurrent discharge was performed thereon with a constant current of 0.1 Cuntil a voltage thereof reached 3 V. For the second charge/dischargecycle, the cell was charged with a constant current of 0.2 C until avoltage thereof reached 4.1 V, and maintained at a constant voltageuntil a current thereof reached 0.05 C. Once the cell charging wascompleted, after a rest period of about 10 minutes, constant currentdischarge was performed with a constant current of 0.2 C until a voltagethereof reached 3 V.

When the cell was charged with a constant current of 1 C until a voltagethereof reached 4.1 V, and maintained at a constant voltage until acurrent thereof reached 0.05 C, the lifespan evaluation was performedthereon. Once the cell charging was completed, after a rest period ofabout 10 minutes, constant current discharge was performed thereon witha constant current of 1 C until a voltage thereof reached 3 V, and sucha cycle was repeatedly performed for the evaluation.

The results of the evaluation of the charge/discharge characteristicsare shown in FIGS. 10A, 10B, and FIG. 11 . FIGS. 10A and 10B showresults regarding characteristics of capacity-dependent electrodepotential changes of the lithium metal batteries of Example 9 andComparative Example 3, respectively.

FIG. 11 shows results regarding capacity changes and efficiencycharacteristics of the lithium metal battery of Example 9.

Referring to FIG. 10B, it was confirmed that, when the cell includingthe laser-untreated LLZO (Comparative Example 3) was charged/dischargedusing a current density of 0.3 mA/cm² according to the galvanostaticmethod, voltage noise caused by Li shortage was observed during the1^(st) and the 2^(nd) charge cycles.

However, it was confirmed that, when the cell including thelaser-treated LLZO (Example 9) was charged/discharged, as shown in FIG.10A, the charge/discharge cycle was driven without shortage upon Lipenetration. In addition, as shown in FIG. 11 , when charged/dischargedover 50 cycles, the cell showed high capacity retention rate andefficiency characteristics. That is, it was confirmed that the surfaceof the amorphous film formed by the laser patterning had effectivelyprevented the growth and propagation of Li ions through a grain boundaryduring charge/discharge of the cell.

Lithium Metal Battery of Example 15

In the same manner as in the evaluation of the charge/dischargecharacteristics of the lithium metal batteries of Examples 9,charge/discharge characteristics of the lithium metal battery of Example15 were evaluated. A charge/discharge cycle was driven at a currentdensity of 0.5 mA/cm².

The evaluation results are shown in FIGS. 14 and 15 .

FIG. 14 shows results regarding characteristics of capacity-dependentelectrode potential changes of the lithium metal battery of Example 15,and FIG. 15 shows capacity changes and efficiency characteristics of thelithium metal battery of Example 15.

Referring to FIGS. 14 and 15 , it was confirmed that the lithium metalbattery prepared according to Example 15 had excellent electrodepotential, capacity retention rate, and efficiency characteristics whenusing a current density of 0.5 mA/cm².

Evaluation Example 7: Ion Conductivity 1) Ion Conductivity at RoomTemperature (25° C.)

The ion conductivity of the solid electrolytes of Example 4 andComparative Example 1 was examined at room temperature (25° C.). Thesolid electrolyte was placed between two stainless steel plates, and animpedance analyzer was connected thereto to measure alternating currentimpedance. The results are shown in Table 3.

TABLE 3 Ion conductivity at 25° C. (Siemens per centimeter (Scm⁻¹))Example 4 2.5 × 10⁻⁴ Comparative Example 1  1 × 10⁻⁶

Referring to Table 3, it was confirmed that the solid electrolyteprepared according to Example 4 had improved ion conductivity at roomtemperature compared to the solid electrolytes prepared according toComparative Example 1.

2) Ion Conductivity at High Temperature (60° C.)

The ion conductivity of the solid electrolytes of Example 4, Examples 4aand Example 4b was examined at high temperature (60° C.). The solidelectrolyte was placed between two stainless steel plates, and animpedance analyzer was connected thereto to measure alternating currentimpedance. The results are shown in Table 4.

TABLE 4 Ion conductivity at 60° C. (Scm⁻¹) Example 4 1.16 × 10⁻³ Example 4a 1.2 × 10⁻³ Example 4b 1.4 × 10⁻³

Referring to Table 4, it was confirmed that the solid electrolytesprepared according to Example 4, Example 4a, and Example 4b had improvedion conductivity at high temperature.

Evaluation Example 8

-   X-ray diffraction analysis of the LLZO films obtained according to    Examples 3c to 3e was carried out.-   As a result of X-ray diffraction analysis on each LLZO film, the    mixing ratio of each phase was examined, and the results are shown    in Table 5 below

TABLE 5 Composition Example 3c 95 weight percent (wt %) cubic garnet 2wt % La₂Zr₂O₇ 2 wt % cubic La₂O₃ 1 wt % W₃O₈ Example 3d 97 wt % cubicphase 3 wt % La₂Zr₂O₇ Example 3e 99.5 wt % cubic phase 0.5 wt % La₂Zr₂O₇

As described above, according to an embodiment, a solid electrolyte fora lithium metal battery is surface-treated with a laser beam so that anactive area of the solid electrolyte increases, and an amorphous film isformed on a surface of the solid electrolyte. In this regard, when suchthe solid electrolyte is used, interfacial resistance between the solidelectrolyte and a lithium metal negative electrode may be reduced, andgrowth and propagation of lithium ions in the solid electrolyte may beefficiently suppressed.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features, advantages, or aspects within eachembodiment should typically be considered as available for other similarfeatures, advantages, or aspects in other embodiments.

While an embodiment has been described with reference to the figures,various changes in form and details may be made without departing fromthe scope as defined by the following claims.

What is claimed is:
 1. A solid electrolyte, comprising: a lithium ioninorganic conductive layer; and an amorphous phase on a surface of thelithium ion inorganic conductive layer, wherein the amorphous phase isin a form of an amorphous film, wherein the amorphous film has a surfacearea of about 35 cm²/cm³ to about 1×10⁶ cm²/cm³, and wherein a thicknessratio of the lithium ion inorganic conductive layer to the amorphousfilm is from 1:0.001 to 1:0.2.
 2. The solid electrolyte of claim 1,wherein the amorphous phase is in a form of an amorphous film having athickness of about 5 nanometers to about 5 micrometers.
 3. The solidelectrolyte of claim 2, further comprising a semi-crystalline filmcomprising a semi-crystalline phase, wherein the semi-crystalline filmis situated between the lithium ion inorganic conductive layer and theamorphous film, and wherein the semi-crystalline film has a thicknessless than a thickness of the amorphous film.
 4. The solid electrolyte ofclaim 3, further comprising a crystalline phase situated between thesemi-crystalline film and the amorphous film.
 5. The solid electrolyteof claim 1, wherein the amorphous film is in a form of a patternedamorphous film.
 6. The solid electrolyte of claim 1, wherein and thepatterned amorphous film has a surface area of about 200 percent toabout 500 percent greater than a surface area of a same solidelectrolyte in which the amorphous phase is not present.
 7. The solidelectrolyte of claim 5, wherein the patterned amorphous film has a shapecomprising at least one of a plurality of perpendicular lines and aplurality of parallel lines, and wherein the perpendicular or parallellines comprise lines having a line width of from about 10 micrometers toabout 30 micrometers
 8. The solid electrolyte of claim 1, wherein thelithium ion inorganic conductive layer comprises at least one of agarnet compound, an argyrodite compound, a lithium super ionicconductor, a sodium super ionic conductor, lithium nitride, lithiumhydride, a compound having a perovskite structure, and a lithium halide.9. The solid electrolyte of claim 8, wherein the lithium ion inorganicconductive layer comprises at least one of: a garnet ceramic of theformula Li_(3+x)La₃M₂O₁₂ wherein 0≤x≤5, and M is tellurium, niobium, orzirconium, Li_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ wherein 0<x<2 and0≤y<3, BaTiO₃, Pb(Zr_(1−x)Ti_(x))O₃ wherein 0<x<1,Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ wherein 0≤x<1 and 0≤y<1,Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃, Li₃PO₄, Li_(x)Ti_(y)(PO₄)₃ wherein 0<x<2and 0<y<3, Li_(x)Al_(y)Ti_(z)(PO4)₃ wherein 0<x<2, 0<y<1, and 0<z<3,Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂wherein 0≤x≤1, 0≤y≤1, 0≤a≤1, and 0≤b≤1, Li_(x)La_(y)TiO₃ wherein 0<x<2and 0<y<3, Li_(x)Ge_(y)P_(z)S_(w) wherein 0<x<4, 0<y<1, 0<z<1, and0<w<5, Li_(x)N_(y) wherein 0<x<4 and 0<y<2, a glass of the formulaLi_(x)Si_(y)S_(z) glass wherein 0≤x<3, 0<y<2, and 0<z<4, a glass of theformula Li_(x)P_(y)S_(z) glass wherein 0≤x<3, 0<y<3, and 0<z<7,Li_(3x)La_(2/3-x)TiO₃ wherein 0≤x≤1/6, Li_(1+y)Al_(y)Ti_(2−y)(PO₄)₃wherein 0≤y≤1, Li_(1+z)Al_(z)Ge_(2−z)(PO₄)₃ wherein 0≤z≤1, Li₂O, LiF,LiOH, Li₂CO₃, LiAlO₂, a(Li₂O)_(a)—(Al₂O₃)_(b)—(SiO₂)_(c)—(P₂O₅)_(d)—(TiO₂)_(e)—(GeO₂)_(f)ceramic wherein 0≤a≤1, 0b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, and 0≤f≤1,Li₇La₃Zr₂O₁₂, Li₁₀GeP₂S₁₂, Li_(3.25)Ge_(0.25)P_(0.75)S₄, Li₃PS₄,Li₆PS₅Br, Li₆PS₅Cl, Li₇PS₅, Li₆PS₅I, Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃,LiTi₂(PO₄)₃, LiGe₂(PO₄)₃, LiHf₂(PO₄)₃, LiZr₂(PO₄)₃, Li₂NH₂, Li₃(NH₂)₂I,LiBH₄, LiAlH₄, LiNH₂, Li_(0.34)La_(0.51)TiO_(2.94), LiSr₂Ti₂NbO₉,Li_(0.06)La_(0.66)Ti_(0.93)Al_(0.03)O₃, Li_(0.34)Nd_(0.55)TiO₃,Li₂CdCl₄, Li₂MgCl₄, Li₂ZnI₄, and Li₂CdI₄.
 10. The solid electrolyte ofclaim 8, wherein the lithium ion inorganic conductive layer comprises atleast one compound selected from a compound of Formula 1 and a compoundof Formula 1 a:Li_(7−x)M¹ _(x)La_(3−a)M² _(a)Zr_(2−b)M³ _(b)O₁₂   Formula 1Li_(7−x)La_(3−a)M² _(a)Zr_(2−b)M³ _(b)O₁₂   Formula 1a wherein, inFormula 1, M¹ comprises at least one of gallium and aluminum, inFormulas 1 and 1a, M² comprises at least one calcium, strontium, cesium,and barium, M³ comprises at least one of aluminum, tungsten, niobium,and tantalum, and 0≤x<3, 0≤a≤3, and 0≤b<2.
 11. The solid electrolyte ofclaim 10, wherein a dopant is the M¹, M², and M³ of Formulas 1 and 1a,and wherein a total content of the dopant in the amorphous phase isequal to or less than 1 mole percent, based on 100 mole percent of theamorphous phase.
 12. The solid electrolyte of claim 10, wherein thecompound of Formula 1 is at least one ofLi_(4.9)La_(2.5)Ca_(0.5)Zr_(1.7)Nb_(0.3)O₁₂,Li_(4.9)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ wherein 0≤δ≤1.6,Li_(6.4)La₃Zr_(1.7)W_(0.3)O₁₂, Li₇La₃Zr_(1.5)W_(0.5)O₁₂,Li₇La_(2.75)Ca_(0.25)Zr_(1.75)Nb_(0.25)O₁₂, Li₇La₃Zr_(1.5)Nb_(0.5)O₁₂,Li₇La₃Zr_(1.5)Ta_(0.5)O₁₂, Li_(6.272)La₃Zr_(1.7)W_(0.3)O₁₂, andLi_(5.39)Ga_(0.5+δ)La₃Zr_(1.7)W_(0.3)O₁₂ wherein 0≤δ≤1.1.
 13. The solidelectrolyte of claim 1, wherein the solid electrolyte is aliquid-impermeable layer having a porosity of 30% or less.
 14. The solidelectrolyte of claim 1, wherein a thickness of the solid electrolyte isabout 1 micrometer to about 300 micrometers.
 15. A lithium batterycomprising: a negative electrode; a positive electrode; and the solidelectrolyte of claim 1 between the negative electrode and the positiveelectrode.
 16. The lithium battery of claim 15, wherein the amorphousphase of the solid electrolyte is adjacent to the negative electrode,the amorphous phase of the solid electrolyte is adjacent to the negativeelectrode, or the amorphous phase of the solid electrolyte is adjacentto the negative electrode and the positive electrode.
 17. The lithiumbattery of claim 15, wherein the negative electrode is a lithium metalnegative electrode comprising lithium metal or a lithium metal alloy.18. The lithium battery of claim 15, wherein an interfacial resistancebetween the lithium metal negative electrode and the solid electrolyteis about 10 ohm cm² to about 500 ohm cm².
 19. A method of preparing asolid electrolyte, the method comprising: providing a lithium ioninorganic conductive layer; and irradiating the lithium ion inorganicconductive layer with a laser beam to form an amorphous phase on asurface of the lithium ion inorganic conductive layer to prepare thesolid electrolyte of claim 1, wherein the irradiating comprisesdirecting the laser beam to form a pattern on the lithium ion inorganicconductive layer, wherein a surface area of the amorphous phase is about200% to about 500% of a surface area of the lithium ion inorganicconductive layer prior to irradiation.
 20. A solid electrolyte,comprising: a lithium ion conductive layer comprising a lithium ionconductive garnet; and an amorphous lithium-lanthanum-zirconium oxide ona surface of the lithium ion conductive layer, wherein the amorphouslithium-lanthanum-zirconium oxide is in a form of an amorphous film,wherein the amorphous film has a surface area of about 35 cm²/cm³ toabout 1×10⁶ cm²/cm³, and wherein a thickness ratio of the lithium ioninorganic conductive layer to the a morphous film is from 1:0.001 to1:0.2.